Problem: Add.
Solution: There are many ways to solve this problem. Let's see two ways we can solve it. Place value table Let's line up the numbers by their decimal places. Tens Ones $.$ Tenths $4$ ${7}$ $.$ ${0}$ $2$ $1$ $.$ ${5}$ Because ${47}$ is a whole number, we can add a decimal point and a $0$ behind to make the columns align. Now, let's add each place value column. Tens Ones $.$ Tenths $4$ ${7}$ $.$ ${0}$ $+$ $2$ ${1}$ $.$ ${5}$ $\underline{~~~~}$ $\underline{~~~~}$ $\underline{~~~~}$ $\underline{~~~~}$ $6$ $8$ $.$ $5$ Decomposing the numbers We can group the whole numbers together and the decimals together. $\begin{aligned} &({47} + {21}) + {0.5}\\\\ &=68 + {0.5}\\\\ &=68.5 \end{aligned}$ $68.5 = 47 + 21.5$